Effects of coiling temperature on microstructure and mechanical propertiesof high-strength hot-rolled steel plates containing Cu, Cr and Ni

In this study, four kinds of high-strength hot-rolled steel plates were fab ricated with additions of tramp elements of Cr and Ni to a basic C-Mn-Si-Cu steel, and their microstructures and mechanical properties were investigat ed to analyze the effects of coiling temperature and tramp elements. When t he steels were coiled at 400 degrees C, their volume fraction of retained a ustenite was lower than the case of coiling at 450 degrees C. The steels co ntaining Cr individually or together with Ni had the volume fraction of ret ained austenite above 10%, but showed the characteristics of dual phase ste els having high tensile strength and low elongation as a large amount of au stenite was transformed to martensite during cooling. In the case of coilin g at 450 degrees C, both elongation and strength-elongation balance were in creased owing to the increase in the fraction of retained austenite and the transformation induced plasticity (TRIP) effect. The addition of Ni result ed in a great increase in the fraction of retained austenite at the higher coiling temperature, thereby improving tensile strength and elongation.